<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<div id="app" class="danger primary">111</div>
		<script type="text/javascript">
			let app = document.getElementById("app")
			app.setAttribute('class', 'zhang qian feng')
			console.log(app.classList)
			console.log(app.classList.contains('zhang'))
			app.classList.add('age')
			app.classList.remove('feng')
			
		</script>
	</body>
</html>
